Wireless communication devices, such as mobile devices and base stations, include transmitter and receiver circuits (i.e., transceivers) and processors to process a wide variety of information in a wide variety of formats. In order to handle such a wide variety of information in such complex communication devices, a conceptual ‘communications’ model has been developed. The communications model characterizes and standardizes the communication functions of a telecommunication or computing system without regard of their underlying internal structure and technology. It is known as the Open Systems Interconnection model (OSI Model) of the International Organization for Standardization (ISO), maintained by the identification ISO/IEC 7498-1, and describes interoperability of diverse communication systems with standard protocols. The model partitions a communication system into abstraction layers.
A layer serves the layer above it and is served by the layer below it. For example, a layer that provides error-free communications across a network provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that comprise the contents of that path. The lowest layer, (Layer 1 (L1)) is known as the Physical Layer and defines the electrical and physical specifications of the data connection. It defines the protocol to establish and terminate a connection between two directly connected nodes over a communications medium and may define the protocol for data flow control.
The layer above, i.e. Layer 2 (L2), is known as the Data Link Layer, which provides node-to-node data transfer between two directly connected nodes, by detecting and possibly correcting errors that may occur in the physical layer. The data link layer is divided into two sublayers: Medium Access Control (MAC) layer, which is responsible for controlling how devices in a network gain access to data and permission to transmit it; and Logical Link Control (LLC) layer, which controls error checking and packet synchronization.
Thus, a complex wireless communication device such as a base station, for example a long term evolution LTE™ base station (sometimes referred to as an eNodeB) includes two major functional components supporting L1 and L2 functions. The L1 functions are connected to the radio interface and follow strict real time demands. The L2 functions are less time critical. However, L2 messages are a dependency for L1.
FIG. 1 is a simplified diagram of a known L1-L2 message sequence chart 100 of a base station showing a loss of time-synchronization and its consequence. The L1 and L2 functions must be time-synchronized in an LTE communication device, for example time-synchronized within an LTE sub-frame (1 msec resolution). As illustrated, L1 frames 108 are synchronized to L2 frames 106. Every LTE Sub-Frame L1 sends a message 110 and the L2 responds in a message 112. Each message contains a System Frame Number (SFN) 102 and Sub-Frame (SF) counter value 104 identifying the Sub-Frame (0-9) being routed between the L1 and L2. A L1 processor compares the SFN and SF counter value of L2 response messages 112 with expected values.
As illustrated, when the L1 message is received at L2, no response is sent at 114 due to an internal L2 delay. The next SF counter value is sent in one or more skipped Sub-Frame(s) at 116, depending on the L2 delay. As there is no match, the L1 processor concludes that L1-L2 time-synchronization is lost, resulting in an out-of-sync error 118 that is generated and sent to the L2 processor in 120, which happens when L2 processing is delayed. Subsequent messages 117 from L1 and responses 122 from L2 continue to be out of time-synchronization with each other. Currently, in response to a loss of time-synchronization, a full system restart is performed in order for the communication device to recover from synchronization loss. A full system restart terminates base station (e.g. LTE™ eNodeB) services for a number of minutes, which is deemed unacceptable to service providers.